Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$74.35	12.625%	$83.7367	$83.74	$83.75	$83.70
Purchase #2	$223.46	6.734%	$238.5078	$238.51	$238.50	$238.50
Purchase #3	$67.38	3.484%	$69.7275	$69.73	$69.75	$69.70
Purchase #4	$76.25	9.829%	$83.7446	$83.74	$83.75	$83.70
Purchase #5	$101.78	9.842%	$111.7972	$111.80	$111.80	$111.80
Purchase #6	$53.79	6.147%	$57.0965	$57.10	$57.10	$57.10
Purchase #7	$156.85	10.360%	$173.0997	$173.10	$173.10	$173.10
7 purchase totals =	$753.86		$817.7100	$817.72	$817.75	$817.60